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my '99 STS is running great at 141000 miles, except for the codes.

P0146, heated oxygen sensor(HO2S) circuit insufficient activity bank 1 sensor 3. does that mean that i need to buy a new sensor or is there something else that i should check.

U1064, loss of communications with DIM. I have no clue!!

any help would be great.

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DIM is Dash Integration Module. If it's a History code, ignore it.

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From your FSM:

DTC U1064 Loss of Communications with DIM

Refer to Data Link Connector (DLC) Schematics

Circuit Description

The class 2 serial data line communicates information between modules. Each module connected to the serial data line is assigned a recognition code, or address. This code is used in order to identify which modules are communicating. Modules communicate with each other by periodically sending state of health (SOH) messages. When the ignition switch is in RUN, each module communicating on the serial data line sends a SOH message every 2 seconds. This ensures that the system is operating properly. When the dash integration module (DIM) stops communicating on the class 2 serial data line, the SOH that is normally sent on the serial data line every 2 seconds disappears. The module, which expects to receive that message, detects the absence of the message. The module in turn sets DTC U1064 associated with the loss of SOH of the DIM.

Conditions for Setting the DTC

The module does not receive a state of health (SOH) message back from the DIM. The module retries the request 3 times, and then sets DTC U1064.

This DTC only sets if U1300 or U1301 is not current.

Action Taken When the DTC Sets

DTC U1064 is stored in the module.

The module uses the default values for the initialization data.

This DTC does not cause driver warning message to appear.

Conditions for Clearing the DTC

This DTC clears (status changes from current to history) under any of the following conditions:

The module detects a state of health message from the DIM.

At each ignition cycle.

A history DTC clears after 50 consecutive ignition cycles if the conditions for setting the DTC are no longer present.

Current and history DTCs may be cleared using a scan tool.

Diagnostic Aids

DTC U1064 does not normally represent a failure within the module.

When loss of class 2 serial data communication DTCs (DTCs with the letter U as the prefix) are stored as history DTCs, know all possible serial data DTCs set in each module before diagnosing the serial data line.

If U1064 is stored in the module memory, inspect for the same DTC stored in other modules capable of storing this DTC.

If the DTC is a history DTC, the problem may be intermittent.

Test Description

The numbers below refer to the step numbers on the diagnostic table:

U1064 is the result of loss of communication with the dash integration module (DIM). Note that other modules on the class 2 serial data line may also set U1064 if the DIM is not communicating with the serial data line.

Clear all DTCs after the repair procedure is complete.

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my '99 STS is running great at 141000 miles, except for the codes.

P0146, heated oxygen sensor(HO2S) circuit insufficient activity bank 1 sensor 3. does that mean that i need to buy a new sensor or is there something else that i should check.....

It might feel like it is running great but if your fuel mileage has dropped, there is a chance your engine is not being toggled to closed loop operation.

That particular sensor is directly aft of the catalytic converter. Crawl under there and check the condition of the shield covering the wire harness; be sure the shield is not damaged and causing damage to the wire harness.

There are some voltmeter tests you can run that require the use of a high impedance voltmeter if you want to go that far.

It might be worth trying to heat soak the entire exhaust system. Take a two hour drive at Interstate speeds with the gear selector in 3. But I would plan on replacing the sensor.


Drive your car.

Use your cell phone.


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i crawled under the car, everything looked good until i decided to to unplug the sensor. the conector is corroded. i cleaned it up as best as i could and put it back together. the dealership wants $130.00 for a new sensor. should i go ahead and replace it because of the corrotion and if i do the wireharness is also corroded what should i do about that?

What does heat soak the exahust system mean?


I'm still trying to figure out WarrenJ's post????

it is a history code and i'll probabably leave it alone for now

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heat soaking....getting the exhaust hot, a long long drive, most of our trips are short not allowing the ex to complaetely heat and remove all moisture.... this can also help with cat converters they love thise long highway rides....

clean them up as best as you can use some dilectric grease when plugging back in, several days will tell if problem corrected.....there are replacement pigtail's available to repair the corodded harness.....suggest you solder and use shrink tubing for repair....not an enviorment for crimp connectors.

agreed if its in history leave it alone,

INFO ...communication codes are common with remote starters.

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Don't solder the wires on the O2 sensor. There is a special kit required to replace it. There was a discussion about this on cadillacowners.com. A tech explained why, though I don't remember enough about it to explain it here.

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